The present invention relates to a flat electrical cable and in particular to a shielded twisted pair flat electrical cable.
Flat electrical cables are increasingly employed as information processing requirements include the parallel transport of several signals from one component to another. Communications, data processing and other applications require precise control over electrical characteristics such as impedance, capacitance, cross talk and attenuation. In particular it is necessary to isolate individual conductors and circuit pairs from extraneous electrical fields and to minimize signal loss from the circuit pairs.
One approach to limiting signal loss and distortion is to shield individual conductors or circuit pairs. A variant of this approach is disclosed by Harlow in U.S. Pat. No. 4,234,759 and by Schumacher in U.S. Pat. No. 3,775,552, in the form of ribbon-shaped assemblies of minature coaxial cables. A disadvantage of individual shielding is that it is expensive.
A more economical approach is to shield the flat cable conductors as an entirety as disclosed by Angele et al in U.S. Pat. No. 3,612,743. A disadvantage of this approach is that cross talk between adjacent conductor pairs with the flat cable is not inhibited.
Another economical approach is to form twisted conductor pairs so as to cancel distorting influences upon each circuit pair. The disadvantages of this approach include limited effectiveness of the cancellation and high attenuation due to lack of means to prevent signal loss. Further it is known to include sections of untwisted conductors periodically in flat cables to facilitate connections. It is also known to provide accurate spacing of the conductors of flat electrical cables so that critical electrical parameters such as inductance and capacitance can be controlled, as disclosed by Lang in U.S. Pat. No. 4,034,148, wherein the insulated conductors or twisted pairs are laminated between plastic films.
Accordingly, it is a primary object of the present invention to provide an improved economical cable with low attenuation and good resistance to signal distortion and which permits precise control over electrical parameters.